#include <stdio.h>
int main()
{
	int a,b,c;
	float s = 0,p;
	scanf("%d%d%d",&a,&b,&c);
	if(a+b>c||a+c>b||b+c>a)
	 {
	 	 p = (a+b+c)/2;
	 	 s = sqrt(p*(p-a)*(p-b)*(p-c));
	 	 printf("%f",s);
	  } 
	else
	printf("no answer");
	
	return 0;
 } 
